Polyurethane foam may be formed by mixing an isocyanate compound with a hydroxyl-containing material, such as a polyol (i.e., a compound that contains multiple hydroxyl groups), typically in the presence of water and a catalyst. As the isocyanate and polyol foam precursors react to form polyurethane, the water reacts with isocyanate to produce carbon dioxide gas, which acts as a blowing or foaming agent to expand the polyurethane into a foamed cellular structure (i.e., a polyurethane foam).
With foam-in-bag packaging, the foam precursors may be mixed and dispensed into flexible plastic bags, for example, as the bags are formed from plastic film. As the precursors react to form expanding foam within the bag, the bag may be sealed closed. The bag may then be placed into a box holding an object to be cushioned. The foam tends to expand within the bag into the available space inside the box to form custom foam cushions around the packaged object. Machines for producing foam-in-bag cushions are described, for example, in U.S. Pat. Nos. 4,800,708; 4,854,109; 5,376,219; 5,727,370; 6,003,288; 6,550,229; 6,675,557; and U.S. Patent Application Publication No. 2012/0261028 A1 published 18 Oct. 2012 (U.S. Ser. No. 13/497,152), each of which is incorporated herein in its entirety by reference.
The liquid isocyanate foam precursor and similar compounds can crystallize upon exposure to the water moisture contained in air. This can cause a problem in the transition points within a system that transports and dispenses the liquid isocyanate foam precursor, where the liquid may be exposed to air. For example, when dispensing liquid isocyanate into a bag, a valve may be the transition point for the liquid isocyanate foam precursor from an enclosed environment (e.g., a storage bottle and/or a pump) into contact with air. If the transition point is the seat of a valve, then the crystallized material may collect at the valve seat to disrupt the valve performance, and may cause the need for cleaning the crystallized material from the valve seat. The cleaning process itself may damage the valve. While a solvent (e.g., tri(propylene glycol) methyl ether) may be used to clean the crystallized precursor from the valve, the use of such a solvent requires additional capital expenditure and/or additional processing steps, and may not remove all the crystallized material.